In recent years, there have been developed a wide variety of vehicles (hereinafter simply referred to as eco-run vehicles) each of which is provided with an internal combustion engine (hereinafter simply referred to as an engine) which can operate an idling stop system and an economy running system for the purpose of realizing a fuel-efficient driving and preventing environmental deteriorations such as global warming. As one of the representative environmentally friendly vehicles as such, there has so far been developed a hybrid vehicle having driving power sources including an engine and an electric motor.
The eco-run vehicle and the hybrid vehicle as previously mentioned are each provided with a control apparatus which can perform a so-called idling stop control to automatically stop the engine when the vehicle temporarily stops for example while the vehicle is waiting the traffic lights, and subsequently to restart the engine for the vehicle to restart moving. The hybrid vehicle has a control apparatus which is generally provided with an electric motor in addition to the engine as driving force sources, so that the vehicle control apparatus can control the automatic stop and restart of the engine in response to the driving conditions of the vehicle while the vehicle is travelling. The eco-nm vehicle and the hybrid vehicle are operated to reduce an unnecessary driving of the engine, thereby making it possible to achieve improved fuel consumption, reduction of exhaust gases, and reduction of noises.
In each of the eco-run vehicle and the hybrid vehicle, a driver's driving intention is indicated to the vehicle control apparatus by losing the brake depression force that shows the depression force of the brake pedal or by generating the accelerator depression force that shows the depression force of the accelerator pedal while the engine is stopped. When a predetermined restart condition is established while the driver's driving intention is indicated to the vehicle control apparatus, the vehicle control apparatus is required to immediately restart the engine.
In order to restart the engine in a short time, it is preferable that the amount of residual exhaust gas remaining in each of cylinders be as small as possible. One of the eco-run vehicles provided with such a vehicle control apparatus has so far been developed to facilitate discharging the exhaust gas in the cylinders with the increased opening degree of the throttle valve before the engine is stopped (see for example Patent Document 1).
The above conventional vehicle control apparatus is constructed to have a throttle valve temporarily opened to a relatively large predetermined opening degree in the engine stop routine. The throttle valve thus temporarily opened results in the fact that the amount of intake air is temporarily increased after a somewhat later time, and the amount of air to be sucked into each of the cylinders is increased before the engine is stopped. Therefore, the exhaust gas is discharged from each of the cylinders while the crankshaft of the engine is being rotated several revolutions by its inertia immediately before the engine stops, so that the air in the cylinder is practically replaced by fresh air. This means that the fresh air having pressure close to the atmospheric pressure comes to be filled in all of the cylinders after the engine stops. As a result, the restart performance of the engine can be improved.